Solenoid valve injectors may be used in internal combustion engines including a so-called common-rail system. In these systems, fuel is injected by electrically activating a solenoid valve, whereby the same is either opened or closed. This creates pressure conditions in the injector based on which a spring-restored nozzle needle is lifted and thus the injection process is initiated. The start of the delivery is established via the opening point in time of the solenoid valve. The fuel metering takes place between the start of the delivery and the closing point in time following the end of the activation of the solenoid valve during a time period referred to as the delivery duration.
Due to the high accuracy requirements with respect to the injection amounts in modern engines, it is necessary to preferably precisely adhere to the particular opening or closing points in time of the solenoid valves in order to precisely meter the amount of the supplied fuel.
In solenoid valve injectors, previously a current level (in particular for the holding current) was ascertained and established during a development phase, which is then later predefined as the setpoint value during operation in the internal combustion engine. For this purpose, the setpoint value is stored in a control unit, for example, in particular in an engine control unit, and set during activation. The injector then usually remains opened for the duration of the activation (energization).
However, aging effects, deposits, in particular fuel deposits, increased fuel viscosity, seat wear and the like may cause a magnetic force demand for keeping the solenoid valve injector open to rise during the operation. However, since the current level is stored as a fixed setpoint value, it is possible that the solenoid valve injector closes prematurely, i.e., even during the activation. This results in a reduced injection amount and thus negatively influences the running behavior of the internal combustion engine.
A method for compensating a control current for a solenoid control valve is known from German Published Patent Application No. 10 2007 058 230, in which a deviation of a magnetic force is compensated for by adjusting the current level of the control current.
A method for ascertaining an adapted control signal, for example for solenoid injectors, is known from German Published Patent Application No. 10 2007 057 144, in which the adapted control signal is iteratively ascertained.
It is therefore desirable to provide an option for deliberately adapting the magnetic force required for keeping a solenoid valve open.